Measuring blood analytes, such as oxygen, carbon monoxide, methemoglobin, total hemoglobin, glucose, proteins, glucose, lipids, a percentage thereof (e.g., saturation) and other physiologically relevant patient characteristics can be difficult. Consider for example, the measurement of blood glucose. Invasive techniques used to measure glucose levels can be painful and inconvenient to perform. In addition, some patients, such as elderly or infant patients, cannot reliably perform these invasive tests on their own. These shortcomings can be especially significant in diabetic patients who require frequent monitoring. Failure to properly monitor and control blood glucose level can have serious consequences for a diabetic patient.
Considerable efforts have been made to develop noninvasive techniques for measuring blood glucose. For example, one noninvasive technique that has been attempted is infrared spectroscopy. With infrared spectroscopy, blood glucose is measured based on the amount of optical radiation absorbed, transmitted, or reflected from the patient's tissue.
Unfortunately, blood glucose can be difficult to measure using traditional infrared spectroscopy. Biologic tissue and water have a high intrinsic absorption at the same wavelengths of light that are responsive to blood glucose. Blood glucose also exists in relatively low concentrations. Furthermore, different patients will have large variations in the optical properties of their skin and blood composition. In addition, any physical movement of the measurement site introduces noise in the measurement signal, making an accurate reading very difficult. These and other challenges have made noninvasive glucose monitoring difficult.
The issues exist beyond the measurement of glucose. In certain conditions, similar problems may exist for the measurement of other analytes, such as oxygen, carbon monoxide, methemoglobin, total hemoglobin, glucose, proteins, glucose, lipids, a percentage thereof (e.g., saturation) or for measuring many other physiologically relevant patient characteristics.